Efficient biosynthesis of 5-aminolevulinic acid from glutamate via whole-cell biocatalyst in immobilized engineered Escherichia coli

5-Aminolevulinic acid (ALA), a natural plant growth regulator, herbicide, insecticide, and photodynamic therapy drug, has various applications in agriculture and medicine. Currently, ALA mainly relies on chemical synthesis; however, this method is unsustainable and cannot meet the increasing demand because of its low yields. In this study, through phylogenetic analysis and the statistic of gene numbers downstream to hemA, we selected 4 candidate hemA genes with high potential for ALA production from genome sequences of 562 bacterial strains and found that hemA from Burkholderia caryophylli had the best effect on ALA production. Next, we found the match of HemA and homologous glutamyl-tRNA^Glu, and further properly overexpressing gltX and tRNA^Glu increased glutamyl-tRNA^Glu recognition by HemA. Moreover, through the rational combination of gene elements from B. caryophylli (hemA, tRNA^Glu) and Salmonella typhimurium (gltX, hemL), optimizing the gene expression model, as well as E. coli hosts, the efficiency of ALA synthesis through the C5 pathway was significantly enhanced in engineered E. coli BurAt-SalSL1 (T7). Finally, we developed a whole-cell bioconversion system to produce ALA for the first time and 20.89 g ALA was obtained from 42.42 g glutamate with a conversion of 63.51% after six catalytic recycles. Overall, our study provides an alternative route for the green production of ALA.